Understood, thank you for your replies. Hadders, I totally understand the frustration of someone wanting to ask for advice, getting it, then wanting to remove their post and thereby reduce the utility of these forums. I didn't plan to do this (planning to ask for this thread to be deleted after receiving advice), I understood that posting here meant having it open to the public eye. I was just posting first to understand the risk vs reward of posting details, which seems to be overwhelmingly positive as you outline and as I have seen on previous posts. And I'd like to thank you all kind people in advance for using your free time to help people like us trying to fix bad situations of our own making.
I took the elizabeth line from liverpool street to slough for which I didn't have a valid ticket. On arrival I tried to buy a ticket from eton&windsor to slough to get through the barriers at slough, which didn't work. The GWR employee (don't know if their role was RPI exactly) questioned me and I lied at first saying I had arrived on this eton&windsor train, which hadn't arrived at slough that morning as they highlighted to me. I then confessed that I had bought it just then to attempt to avoid the fare, because I knew the slough station was outside of oyster system and I hadn't bought a valid ticket. They asked to scan my oyster and took a picture of my recent trainline history, so I obliged to both and cooperated with taking name and address details. Received the reported for prosecution note, and discussed with them what the consequences could be (I was stupidly completely unaware of the seriousness of this). They informed me GWR usually tries to settle out of court but they couldn't guarantee this would be the case, understandably that requires a full investigation before they choose next steps as I've read on this forum.
They are likely to suspect ~8 previous instances of short faring, with fraudulent refunds applied, mostly on GWR but one on another TOC and one more on another TOC. These are quite sporadic but over a few years of trainline history since 2021 which is probably an aggravating factor. However, one of these is actually a legitimate one where I replaced the journey with a coach ticket which doesn't show in the trainline records, but if I'm lucky enough to get a settlement offer I don't imagine trying to dispute this makes much sense.
Does anyone have an estimate on how long the GWR letter (if I'm luck enough to get the "give us your version of events" letter and not an immediate court summons notice) usually gives to reply to them? I'm supposed to go away from 7-12th April so I wonder if I will have to cancel this, although it's probably unlikely to arrive on Sunday 7th, that would put me 5 days away from the mailbox, only able to check it on the evening of the 12th. However, I can definitely get my flatmate to check our shared mailbox for me but that's obviously less than ideal having to involve him in my personal issues. Also curious to know whether they will be able to see trainline booking transaction times and see when they were scanned, I'm assuming they can.